The present invention relates to a brush holder for use with electric actuating devices.
Prior to the present invention, a certain style of brush holder for electric actuating devices (such as rotating or linear moving electric apparatus, dynamos, motors, and generators) incorporated a cartridge-style brush holder providing for an externally replaceable brush. Because of prior design limitations and space considerations, the prior cartridge-style brush holders necessitated using a brush which utilized a helical coil compression spring to push the brush towards the rotating or moving surface of the electric device. A helical coil compression spring, however, provides uneven and erratic pressure on the brush during the life of the brush, because as the brush wears down, the helical coil spring decompresses (xe2x80x9crelaxesxe2x80x9d) and the spring pressure decreases resulting in an erratic rate of wear as the brush gets shorter due to the declining spring force. This leads to less than optimal performance, decreased life of the brush, more frequent and costly replacement of the brushes and increased maintenance on the electric device. Additionally, the helical coil compression spring takes up a disproportionately large amount of interior space inside the brush holder that could otherwise be utilized by a longer brush. One solution to this problem was the introduction of a constant force spring. By providing a constant force of spring pressure to the brush, the brush will exhibit a consistent wear rate, a constant rate of pressure of applied force to the brush, reduced wear of the contact surface, longer brush life, more optimal device performance and lower overall maintenance costs. However, the brush holder assemblies incorporating constant force springs were completely internal to and wholly encapsulated in the electric actuating devices, as shown in U.S. Pat. No. 2,695,968 to Welch et al., and not in a cartridge-style brush holder with an externally replaceable brush.
While still providing and augmenting the principal advantages of the cartridge-style brush holder with an externally replaceable brush, the present invention: (1) allows for the longest brush possible to be utilized in any particular electric actuating device given the device""s particular dimensions, resulting in the longest possible brush life and device life; (2) permits ease and efficiency of assembly into the electric actuating device; (3) provides a robust and durable design; (4) reduces replacement and maintenance costs; and (5) allows for the brush to be easily replaced externally without the undue labor, cost, damage and danger of disassembling and attempting to maintain the electric actuating device. In fact, a constant force cartridge-style brush holder with an externally replaceable brush allows for an even longer brush than could previously be achieved because the constant force spring utilizes less interior space in the brush holder than the helical coil compression spring system that existed before. This space can now be utilized by additional brush length.
One prior art reference, U.S. Pat. No. 5,463,264 to Koenitzer (the ""264 patent) attempted to incorporate one type of constant force spring brush assembly into a cartridge-style brush holder providing for an externally replaceable brush. However, the ""264 patent when utilized for its intended purpose, was found to have practical manufacturing, application and performance problems. First, because of significant loads exhibited by the brush holder during use, the U-shaped retainer defined by the ""264 patent had a tendency to fracture in several different areas, such as in the recesses (where the material is the thinnest) or along the middle top portion (in an area separating the two legs), at which point the brush holder described in the ""264 patent is rendered unsatisfactory. It is a critical aspect of the invention to replace a worn brush and not a cracked or broken brush holder. It is thus a first objective of the present invention to replace the U-shaped retainer defined by the ""264 patent with a differently designed, more durable, stronger U-shaped shunt.
Second, the ""264 patent includes a single container with slots defined therein for the receipt of the legs of the U-shaped retainer and the brush holder. When assembled, the end of the brush extends directly out of the end of the container for contact with the commutator, leaving a majority of the brush maintained within the container. There is no separate protective interior tube in the ""264 patent. This presents problems during use, as strong vibration forces, high temperatures and noise from the operation of the electric actuating device tend to cause failures and problems in the container and U-shaped retainer. It is thus a second objective of the present invention to provide a means of adequately compensating for the temperature, noise, and vibrations generated by the brush and the operation of the electric actuating device.
Third, the ""264 patent describes a cylindrical container with a pair of longitudinally extending slots for directly receiving the retainer and the brush. This cylindrical container is preferably made out of an insulating, non-conductive material such as plastic. The container described in the ""264 patent would not provide for optimal device performance, because the brush would not optimally travel through the slot of the container due to less than optimal tolerancing and surface texture of the slots in the container due to the nature and composition of the material comprising the container. This would cause an uneven an unpredictable rate of brush wear. It is thus an objective of the present invention to provide a superior, more robust brush holder that provides for better device performance and longer brush life, and provides for a smoother brush ride and optimal brush wear during operation of the device.
Lastly, the ""264 patent states that the brush is connected to a shunt (wire) which is further connected to a terminal that fits between a brass strip inserted into a slot in the cylindrical container. While the ""264 patent does not state how the brush holder assembly is connected to an external electrical source (external to the container), it is widely known that some type of terminal connection must be contained in the brush holder assembly and attached to the external electrical source, in order to run electrical current through the brush, to create the magnetic flux and drive the electric actuating device. The ""264 patent fails to provide pragmatic means for which to attach the connection to the external electrical source to the brush holder for running the electrical current through the brush. Typically, a lead wire is crimped to the terminal connection. However, in the ""264 patent, the terminal connection (terminal 34) is connected to the brush (14) and maintained within the container (25). To achieve the external electrical connection, an additional terminal connector would have to be connected in some undescribed fashion to the opposite side of the first terminal connection (34) and placed within the slot formed between the conductive strip (not labeled) and the container 25 [See FIG. 2 of U.S. Pat. No. 5,463,264]. The conductive strip allows the electrical current to flow from the undescribed additional terminal connector (which is connected to the external electrical source) to the terminal (34). With the need for the additional terminal connector, product and manufacturing costs are increased. In addition, this also makes the manufacturing and assembly process more complicated and costly. It is thus an objective of the present invention to provide the optimal means of facilitating the connection of the brush holder assembly to the external electrical source, which is more cost effective, lowers product and manufacturing costs, and provides an easier method of fabrication.
In accordance with the present invention a brush holder for use with an electric actuating device is provided. The brush holder includes a cylindrical sleeve mounted in the housing of the device and having an opening extending radially inward toward a commutator of the device. (As used herein, the term xe2x80x9ccommutatorxe2x80x9d shall include, but not be limited to, commutators, slip rings and any other moving surface onto which or from which an electric current is directed or generated.) The sleeve incorporates a tube that has an end extending inwardly toward the commutator. The tube may have a length longer than the cylindrical sleeve, such that the end extends beyond the opening. A U-shaped shunt, preferably having a uniform thickness, is slidably positioned within the tube. The U-shaped shunt has legs extending radially inward towards the commutator of the device; the legs of the shunt also have flanges extending outwardly therefrom. A brush, preferably, but not limited to, a carbon brush, is positioned between the legs of the shunt with a constant force spring being positioned between the brush and the inner surface of the U-shaped shunt. The constant force spring has a pair of coiled ends that are manually positioned against the flanges. The constant force spring also includes a middle portion that engages the center of one end of the brush in order to resiliently push the brush against the commutator of the electric actuating device with a constant force. The U-shaped shunt is connected to the brush by a pig tail wire.
In addition, the tube has two pairs of longitudinally diametric extending slots, one pair for receiving and positioning the shunt and the other pair for receiving and positioning the brush. Also, a removable cap is positioned within a radially outer end of the sleeve for retaining the shunt, constant force spring and brush within the sleeve during operation of the device. Furthermore, a longitudinal slot is positioned between the tube and the cylindrical sleeve for receiving a terminal connector onto which is crimped a lead wire which in turn is connected to an external electrical source.
The present invention includes a tube (preferably made out of a conductive metallic material, including, but not limited to, brass), within a sleeve (preferably made out of an insulating non-conductive material including, but not limited to, thermosetting and thermoplastic plastic resins). The tube will slidably receive the brush, the constant force spring and U-shaped shunt. The material of the tube is such that it has a greater ability to dampen noise and vibration and dissipate heat during operation than the material used in the prior art. The surface texture of the material of the tube has a greater ability to provide for an optimal brush ride for the brush than the surface texture of the material used in the prior art. This leads to longer brush life and more optimal device performance. The present invention also allows closer, tighter tolerances to be attained than the prior art. This provides for less brush movement, less brush xe2x80x9cchatterxe2x80x9d, less brush dust and significantly reduces the occurrences of arcing and device failure.
Numerous other advantages and features of the invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings.